The present invention relates to an improved energy absorbing device of the type adapted to decelerate an impacting vehicle.
A wide variety of crash attenuators have been used to decelerate an impacting vehicle which has left a highway, including attenuators based on dispersible inertial materials such as sand, valved fluids such as water, disintegrating materials such as vermiculite, and buckling columns. The present invention relates particularly to the last of these approaches.
U.S. Pat. No. 4,339,980 (Van Schie) discloses a crash attenuator which includes spaced apart crumple tubes which buckle to absorb the kinetic energy of a decelerating vehicle. However, these crumple tubes are relatively long and are not diagonally braced, and they often fail in a long column rather than a short column buckling mode. Long column buckling absorbs less energy than short column buckling, and long column buckling is therefore a relatively inefficient failure mode for an energy absorbing element of a crash attenuator.
U.S. Pat. Nos. 4,029,350 (Goupy), 4,154,469 (Goupy) and 4,118,014 (Frosch) all disclose crash attenuators which utilize densely packed columns arranged to buckle in response to a vehicle impact. Because the columns are closely packed rather than spaced apart as in the embodiments described below, it is not possible to use identical columns throughout the crash attenuator while varying the deformability of the attenuator in either the width or the length dimension. As explained below, there are important advantages in readily being able to vary the resistance to deformation of the crash attenuator in both dimensions.
U.S. Pat. No. 4,635,981 (Friton), assigned to the assignee of the present invention, discloses a truck mounted attenuator having an array of parallel diaphragms with foam filled cells situated between the diaphragms.